Two cells, having the same emf, are connected in series through an external resistance `R`. Cells have internal resistance `r_(1)` and `r_(2) (r_(1) gt r_(2))` respectively. When the circuit is closed, the potentail difference across the first cell is zero the value of `R` is

Options

A. `r_(2)-r_(1)`
B. `r_(1)-r_(2)`
C. `r_(1)+r_(2)`
D. `(r_(1)-r_(2))/(2)`

Answer

B

Explanation

`i=(E_(1)+E_(2))/(R+r_(1)+r_(2)),V_(1)=E_(1)-ir_(1)`